Pubdate: Tue, 21 Sep 2010
Source: Montreal Gazette (CN QU)
Copyright: 2010 Canwest Publishing Inc.
Contact: http://www.canada.com/montrealgazette/letters.html
Website: http://www.montrealgazette.com/
Details: http://www.mapinc.org/media/274
Authors: Evra Taylor Levy, Eddy Lang
Bookmark: http://www.mapinc.org/mmjcn.htm (Cannabis - Medicinal - Canada)
Note: Download the study at http://mapinc.org/url/t4KIh82X

DOES MARIJUANA REALLY RELIEVE PAIN?

The use of marijuana for a few carefully selected medical conditions 
has generated heated discussion, pitting those who favour 
legalization against those who warn about the undesired consequences 
of wider availability. Absent from much of the debate so far, 
however, is scientific evidence to establish whether marijuana really 
works to relieve chronic pain; and if it does, whether it does so in 
a manner that is distinct from simply providing the well-known high 
that has made it a popular recreational but illicit drug. This 
edition of Health-Watch takes a closer look at the burden of chronic 
pain and a recent study that has received a great deal of attention.

What is neuropathic pain?

For the sake of differentiation, let's take a look at two main types 
of pain: non-neuropathic and neuropathic. Non-neuropathic pain is 
more common and is caused by such things as bumps, bruises, sprains, 
fractures and inflammation caused by arthritis.

Neuropathic pain, on the other hand, is the result of injury or 
abnormal signals coming from the peripheral nervous system - that is, 
the nerves outside of the brain or spinal cord. Neuropathic pain can 
occur as the result of such conditions as shingles, cancer, phantom 
limb pain, the phenomenon known as entrapment neuropathy - in which a 
nerve is pinched ( as occurs in carpal tunnel or chronic back pain 
syndromes) - and peripheral neuropathy, which is common among diabetics.

The symptoms of neuropathic pain include a constant gnawing pain, as 
well as a shooting and burning sensation, or tingling and numbness. 
No matter how you describe it, its effects can be debilitating, 
causing tremendous physical and emotional suffering and loss of 
quality of life. Not surprisingly, patients who suffer from 
neuropathic pain experience high rates of depression and insomnia. 
Neuropathic pain is frequently chronic, sometimes lasting months or 
even years. While complete cures are unlikely, it can be controlled 
with the proper treatment.

How might THC work?

The substance known as tetrahydrocannabinol ( or THC), which was the 
subject of the study we are looking at, belongs to the family of 
compounds known as cannabinoids, which are closely related to 
pain-relieving molecules released by our own bodies. THC is the 
cannabinoid extracted from the Cannabis sativa ( hemp) plant commonly 
known as marijuana, or pot.

The medical use of cannabis or marijuana is not new. Cannabis sativa 
has been used to treat pain since the third millennium BC. Between 10 
and 15 per cent of patients with chronic pain caused by a variety of 
conditions, including multiple sclerosis, currently smoke cannabis 
for its seemingly helpful effects.

The study

Ware MA, Wang T, Shapiro S, et al. Smoked cannabis for chronic 
neuropathic pain: a randomized controlled trial. CMAJ, August 30, 
2010. DOI: 10.1503/ cmaj. 091414.

What was unique and important about this study?

Investigators at McGill University undertook a remarkable challenge 
in conducting this study. In addition to dealing with the enormous 
regulatory hurdles to performing research on cannabis, the team 
needed to develop a true placebo, or pretend cannabis, that would be 
indistinguishable from the real McCoy to determine the exact effects 
of the THC without a psychological effect. The study tested four 
potencies ranging from the zero per cent placebo dose to a 10 per 
cent THC concentration. The researchers managed to recruit 23 
neuropathic pain patients who were suffering from pain arising from 
an earlier injury or a surgical procedure. They were randomly 
assigned to the four dosing regimens and took a single inhalation of 
the smokable capsules provided to them containing the active 
ingredient or placebo, three times a day for two separate five-day periods.

Of key interest to the researchers was whether there would be a 
reduction in the severity of the pain that the subjects experienced. 
However, the researchers also measured other parameters: levels of 
anxiety, depression and the ability to sleep restfully. The 
investigators also wanted to know whether subjects experienced a high 
from the test drug.

What did the study show?

The highest potency of THC reduced the level of pain by a modest 
amount, while the weaker preparations had only marginal effects. In 
addition, the higher levels of THC improved the subjects' ability to 
fall asleep and led them to report a more restful night. There was no 
apparent effect on overall mood, nor any evidence of this small 
exposure to cannabis leading to a perceived high.

What does this mean for those suffering from neuropathic pain?

While the McGill study is a welcome addition to what is a fairly 
sparse number of well-done studies, there is still more to learn 
about how to make cannabis as acceptable and as safe as possible. In 
the meantime, a patient's autonomy in making the best decision for 
his or her particular circumstance should be paramount, and this 
study provides some guidance in that regard.

How can patients obtain THC legally?

Synthetic cannabinoids are sold in Canada in pill form as Marinol and 
Cesamet. While in most countries it is illegal to smoke cannabis for 
recreational use, as a medicine it is legal in Canada, Germany, the 
Netherlands, Spain and Israel, among other countries. To legally 
smoke marijuana, one has to find a doctor willing to sign a 
prescription for the drug. Health Canada then approves the possession 
licence, and the prescription is filled by growing a small supply of 
marijuana or by buying it from Health Canada. The organization 
estimates that approximately 4,000 Canadians have been granted a 
licence to possess marijuana legally. The material provided in 
Health-Watch is designed for general educational purposes only and 
does not pertain to individual cases. It should not replace necessary 
medical consultations with your own doctor or medical professional.
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MAP posted-by: Jay Bergstrom